The present invention generally relates to combustion apparatus and, in a preferred embodiment thereof, more particularly relates to a specially designed variable firing rate fuel burner.
Fuel burners are utilized in a variety of heating applications in which the burner operates to transfer combustion heat to a heat exchanger to thereby heat a fluid being flowed through the heat exchanger during firing of the burner. In some of these heating applications it is desirable that the pattern of the flame emanating from the outlet of the burner be considerably elongated parallel to the axis of the burner to suit the interior geometry of the heat exchanger and/or to satisfy certain heat transfer efficiency design parameters.
One previously proposed technique used to provide the burner flame with the requisite elongated shape was to coaxially attach to the outlet end of the burner a tubular ceramic flame shaper that axially projected a considerable distance beyond the outlet end of the burner body. While this technique provided the burner flame with the desired elongated shape, it had certain problems, limitations and disadvantages such as being fragile, relatively expensive, and undesirably increasing the overall length of the burner body.
In burner-fired heat exchanger applications of this general type it is often desirable to vary the firing rate of the burner. However, in conventional fuel burner design it is often difficult to substantially reduce the firing rate of the burner without potentially creating undesirable flame xe2x80x9cflashbackxe2x80x9d.
In view of the foregoing it can be seen that a need exists for an improved fuel burner which eliminates or at least substantially reduces the above-mentioned problems, limitations and disadvantages commonly associated with fuel burners of conventional constructions. It is to this need that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, an improved fuel burner apparatus is provided which comprises a body having an outlet end and including a pilot conduit extending along an axis and through which a pilot fuel/air mixture may be flowed, discharged through the outlet end, and ignited to create a pilot flame. An inner firing conduit circumscribes the pilot conduit and laterally defines therebetween a first flow space communicating with the body outlet end. An outer firing conduit circumscribes the inner firing conduit and laterally defines therebetween a second flow space communicating with the body outlet end.
The fuel burner apparatus also includes a fuel/air delivery system operative to force fuel and air through each of the first and second body flow spaces, for discharge through the body outlet end and ignition by the pilot flame, to responsively create a main burner flame. According to a key aspect of the present invention, the burner body is configured in a manner such that the flow of fuel and air discharged from the second body flow space functions to laterally constrain the main burner flame, representatively providing the main burner flame with a relatively thin, axially elongated configuration. The inner and outer firing conduits have downstream ends, and the downstream end of the outer firing conduit is preferably axially offset from the downstream end of the inner firing conduit in a downstream direction to aid in the shaping of the main burner flame.
According to other aspects of the present invention, the fuel/air delivery system is operative to force separate first and second fuel/air mixtures respectively through the first and second burner body flow spaces, and the fuel/air delivery system is operative to utilize different fuels in the separate first and second fuel/air mixtures.
In an illustrated preferred embodiment of the fuel burner, the fuel/air delivery system includes first and second fuel injectors respectively communicated with the first and second flow spaces and operative to receive fuel from at least one source thereof. An air inlet plenum structure is carried by the burner body, and first and second mixing plenum structures extend through the air inlet plenum structure, the first and second mixing plenum structures being respectively coupled to the first and second fuel injectors, having air inlet openings therein, and respectively communicating with the first and second burner body flow spaces. The fuel burner further includes an air delivery structure operatively coupled to the first and second flow spaces, the air delivery structure representatively including an air supply fan having an outlet communicated with the interior of the air inlet plenum structure.
According to another aspect of the present invention, the outlet end of the burner body is operatively coupled to a heat exchanger through which a fluid to be heated may be flowed, the heat exchanger having an interior space for receiving the main burner flame from which combustion heat may be transferred to the fluid being flowed through the heat exchanger. Representatively, the heat exchanger has a series of interior heating tubes through which the fluid to be heated may be flowed, the series of interior heating tubes circumscribing the burner flame-receiving interior space of the heat exchanger and longitudinally extending parallel to the axis of the burner body. The axial elongation of the main burner flame injected into the interior of the heat exchanger parallel to the heat exchanger tubes substantially enhances the overall heat transfer efficiency of the overall fuel-fired heat exchange apparatus.